David Brooks has a great article in the NYTimes explaining that voters derive their values from their party affiliation, not the other way around.
Drawing on a vast range of data, these political scientists argue that party attachment is more like attachment to a religious denomination or a social club. People have stereotypes in their heads about what Democrats are like and what Republicans are like, and they gravitate toward the party made up of people like themselves.
This fits with my experience. I think it explains why the conservative talk show cabal is so influential with their polemic. It's not the arguments that are successful, it's the manner in which those that disagree are emasculated.

I think this also shows why shows like Crossfire are detrimental. Until we foster a culture that encourages respectful disagreement, the issues will be secondary to party affiliation.